I was told that "Fiera" in Spanish means "wild one" and is used as an insult to mean the woman is likely to claw your eyes out, uncivilized, etc. I was also told that in Esperanto fiera is an adjective meaning "proud" (from fiero, which means "pride"). It's not feminine and it's not used as a name. The feminine form would be fierina "she-proud" which doesn't make too much sense and since it is used as a name and a noun it should probably be Fiero or Fierino anyway. Esperanto did not originally use names that end in -a. Indo-European speakers could not grasp the idea of a feminine name that ended in -o so Esperantists allowed for the -a ending, but the -o is still more correct.

Author and English professor Richard Lederer wrote in his book "Fractured English" that a truck with this name had been introduced by Ford Motors to the Spanish-speaking market, only to find that it meant "ugly old woman" in Spanish.